Pruning concord grape vine?

I have a two year old Concord grapevine that I have growing on an arbor. Last year, I read conflicting information on pruning (one source said to prune it and the other saying not to prune its first year)

I have a two year old Concord grapevine that I have growing on an arbor. Last year, I read conflicting information on pruning (one source said to prune it and the other saying not to prune its first year). Since I wasn't sure what to do, I didn't prune it at all. It surprisingly yielded two grapes this past summer-- I wasn't expecting anything at all.

Now that it is two years old, I know enough that it needs to be pruned while it is dormant. However, this weather (warm and cold) confuses me, unsure if it would confuse my plants as well. When do you recommend I prune it?

Also, how should I prune it? Attached is a picture of my unruly grapevine.